JPH0212678B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The disclosed technology belongs to the field of technology for treating the end portion of a unit pipe of a corrosion-resistant double pipe used for piping for corrosion-resistant fluids such as oil country tubular goods.

<Summary of the gist> The present invention is a unit double pipe, such as an outer pipe made of carbon steel and an inner pipe made of stainless steel, with one side being corrosion resistant and the other non-corrosion resistant. For unit double pipes where the pipes are tightly fitted at the general part and not completely metallurgically connected at the end of the pipe, a corrosion-resistant metal such as stainless steel is welded in a ring shape to the end of the pipe. This invention relates to a double tube structure of an end pretreatment welding unit, and in particular, the tube end on the corrosion resistant tube side and the inner surface on the non-corrosion resistant tube side are formed into a ring shape with a tensile force applied to the non-corrosion resistant tube side. The ends of both tubes are metallurgically joined together by metal welding, and then the inner surfaces of the inner and outer tubes are machined to form a joint while compressive residual stress is generated in the corrosion-resistant tube. This invention relates to a double pipe structure of an end pretreatment unit formed flush with each other.

<Prior art> As is well known, corrosive fluid pipes such as oil country tubular goods and nuclear power plant piping have pressure resistance, heat resistance, corrosion resistance,
In order to provide wear resistance, for example, a double tube is used, in which the outer tube is made of a non-corrosion resistant carbon steel tube, the inner tube is made of a corrosion resistant stainless steel tube, etc., which are joined in a predetermined manner to form a single layer.

For on-site piping, for example, as shown in FIG. There is a mode in which they are connected together.

Of course, in addition to welded joints, coupling joints and flange joints may also be used.

By the way, the length of the unit double pipe 3 is limited due to the conditions of the equipment at the time of manufacture and restrictions on transportation to the site. the second depending on the length of time
As shown in the figure, there is a possibility that corrosion 7 may invade the interface 6 between the inner and outer tubes 1 and 2 at the tube end 5.

Generally, the pipe end 5 is mechanically processed by forming a joint surface 8 during manufacturing at a factory.
This is because the inner and outer pipes 1 and 2 are not metallurgically connected, and therefore corrosion progresses during open storage and sea transportation.

<Problem to be solved by the invention> To deal with this, measures such as fitting a cap or the like to the end of the pipe have been attempted, but the effectiveness varies in degree and it has not been possible to completely prevent the progress of corrosion. The drawback was that I couldn't do it.

As mentioned above, at the tube end 5 of the unit tube 3, the inner and outer tubes 1 and 2 are not completely mechanically and metallurgically connected and are not integrated, so there is a so-called notch. This effect appears, and due to competing complex conditions such as the difference in thermal stress during welding and bonding with the weld metal, a boundary 6 between the inner and outer pipes 1 and 2 is formed at the welded part 4, as shown in FIG. There was also a problem where crack 9 occurred.

On the other hand, for example, there are the inventions disclosed in Japanese Patent Publication No. 44-5289 and the inventions disclosed in Japanese Patent Application Laid-open No. 54-78340, but these known inventions are based on welding techniques for actual installation of joints of multiple unit double pipes. This is related to corrosion intrusion into the inner and outer pipes at the end of the pipe when it is left unused for a period of time, such as during the period from manufacturing the unit double pipe of the set length at the factory to installation on site, before fitting. This technique is not a countermeasure, and is inconvenient in preventing the progress of corrosion.

<Objective of the Invention> The object of the present invention is to solve problems such as corrosion intrusion at the pipe end of the corrosion-resistant unit double pipe based on the above-mentioned prior art, and to A ring-shaped metal is preprocessed and welded to at least the corrosion-resistant pipe side of the part to metallurgically connect the two pipes together to prevent corrosion penetration, cracks, etc., and the field of use of piping technology in various industries. It is an object of the present invention to provide a double pipe structure of an excellent end pretreatment welding unit that is beneficial for the following purposes.

<Means/actions for solving the problems> In order to solve the above-mentioned problems, the structure of the present invention, which is based on the scope of the above-mentioned claims in accordance with the above-mentioned object,
Corrosion-resistant unit: At the junction of the inner and outer tubes at the pipe end of a double pipe, a tensile force is applied to the non-corrosion-resistant pipe end on the non-corrosion-resistant pipe side, and a ring-shaped corrosion-resistant metal is placed in a state where tensile stress is formed. When the inner and outer tubes are welded to metallurgically join them together and release the tensile force on the non-corrosion-resistant tube, compressive residual stress is generated in the corrosion-resistant tube, so the tube is machined in preparation for the subsequent joint processing. Processing is done so that the end faces are flush, and since both pipe ends are metallurgically joined together by the pre-treatment welding described above, the boundary between the pipe ends and both pipes is Technical measures have been taken to prevent corrosion from penetrating into the piping, to prevent cracks from occurring during welding, and to prevent stress corrosion cracking from occurring in the corrosion-resistant pipes due to compressive residual stress during pipe operation.

<Example> Next, an example of the present invention will be described below based on the drawings from FIG. 4 onwards. It should be noted that portions having the same features as those in FIGS. 1, 2, and 3 will be described with the same reference numerals.

In the embodiment shown in FIGS. 4 to 7, a unit corrosion-resistant double tube 3 of a predetermined length has an outer tube 1 made of non-corrosion resistant carbon steel and an inner tube 2 made of corrosion resistant stainless steel.
However, for example, the inner tube 2 is made in a multi-layered and integrated manner using the heat expansion method, which is an earlier invention of the applicant, and the inner tube 2 has the inner tube 2 at the tube end as shown in FIG.
The set length is shorter than the outer tube 1, and a stepped portion 10 is formed.

After manufacturing the unit double tube 3, the tube end of the outer tube 1 is clamped and pulled in the axial direction using a hydraulic jack or the like to apply a tensile force to the outer tube 1, as shown in FIG. Overlay welding of stainless steel on the stepped portion 10 1
1 is applied in a ring shape as a pretreatment weld, and the tube end 2' of the inner tube 2 and the tube end inner surface (boundary surface) of the outer tube 1 are integrally metallurgically joined.

Therefore, after the pretreatment welding, the boundary surfaces of the inner and outer tubes 1 and 2 are reliably joined and sealed by ring-shaped overlay welding 11 at the tube end of the unit double tube 3, and the outer tube Upon release of the tensile force on 1, compressive residual stresses are created in the inner tube 2, particularly at its tube ends, which prevent stress corrosion cracking.

In this case, overlay welding 11 of corrosion-resistant metal to the tube end 2' of the corrosion-resistant inner tube 2 is metallurgically compatible with the corrosion-resistant inner tube 2, and the tensile force is applied to the non-corrosion-resistant outer tube 1. On the other hand, the corrosion-resistant inner tube 2 has various advantages such as compressive stress is easily generated and only a small amount of overlay is required.

In addition, applying overlay welding 11 to the inner and outer tubes 1 and 2 at the tube ends basically has the same mechanical and metallurgical incomplete bonding problem as mentioned above, but the unit is double-layered in the factory. When performing overlay welding 11 after manufacturing the pipe 3,
Since it can be carried out under advantageous conditions such as complete equipment and sufficient management, there is no risk of the above-mentioned cracks occurring.

Finally, in the factory, the inner surface of the overlay weld 11 of the pretreatment welding is made flush with the inner surface of the inner tube 2 in preparation for joint connection in the field, as shown in FIG. At the same time, a grooved surface 8 for butt welding is formed on the tube end.

In this state, the inner and outer pipes 1, 1,
It is possible to reliably prevent corrosion from entering through the interface 6' between the two.

When connecting the joints on-site, as shown in FIG.
1, the notch effect shown in FIG. 3 does not occur, and the occurrence of cracks and the like is also prevented.

In addition, in the embodiment shown in FIG. 8, the inner surface of the outer tube 1 is also machined by machining the stepped portion 10 shown in FIG. This is an embodiment in which build-up welding 11 is performed as a pretreatment weld to provide a seal to the interface 6 of the tubes 1 and 2 to provide metallurgical bonding, and the practical effect is the same as that of the above-described embodiment.

It goes without saying that the embodiments of the present invention are not limited to the above-mentioned embodiments. For example, a ring-shaped corrosion-resistant metal is formed separately in advance, and the tube end of a unit tube is bonded by electron beam welding, friction welding, etc. Pretreatment welding may be performed.

<Effects of the Invention> As described above, according to the present invention, at the pipe end of the unit double pipe in which one of the inner and outer pipes of the unit pipe is a corrosion-resistant pipe, the pipe end face of the corrosion-resistant pipe and the inner surface of the non-corrosion-resistant pipe are the same as the non-corrosion-resistant pipe. A corrosion-resistant metal is integrally pre-welded in a ring shape with tensile stress applied to the pipe, and the tensile force on the non-corrosion-resistant pipe is released to create compressive residual stress in the corrosion-resistant pipe, in preparation for on-site joint connection. The inner and outer surfaces of both the inner and outer tube ends are machined to be flush with each other, so that the inner and outer tubes at the tube ends of the unit double tube are reliably joined together metallurgically. This provides an excellent effect in that there is no risk of corrosion occurring and penetrating the tube boundary surface at the end of the unit tube when the tube body is manufactured in a factory and then stored in the open or transported by sea.

In addition, by applying tensile force to the non-corrosion resistant tube side and performing pretreatment welding, compressive residual stress is formed in the corrosion resistant tube of the unit tube body, which has the excellent effect of preventing stress corrosion cracking from occurring during operation.

Furthermore, by pre-welding a corrosion-resistant metal to the end face of the corrosion-resistant tube, the amount of corrosion-resistant metal that is compatible with the corrosion-resistant tube can be reduced, leading to weight reduction, resource conservation, and cost reduction. There is also.

Also, when unit pipes are connected via welded joints, no notch effect occurs, and therefore,
Another advantageous effect is that defects such as cracks do not occur in the welded area.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a welded joint of a double pipe, Fig. 2 is a cross-sectional view of boundary corrosion at the pipe end, Fig. 3 is a cross-sectional view of a crack in a welded joint, and Fig. 4 and the following are explanatory diagrams of embodiments of this invention. 4, 5, 6, and 7 are process sectional views of one embodiment, and FIG. 8 is a sectional view of another embodiment. 1... Outer tube, 2... Inner tube, 6, 6'... Boundary (surface), 5... Tube end, 11... Pretreatment welding (corrosion resistant metal), 3... Double tube.

Claims (1)

[Claims] 1 Unit 2 where one of the joining pipes of the inner and outer pipes of the unit pipe is a corrosion-resistant pipe and the other is a non-corrosion-resistant pipe, and pre-treatment welding is performed on the pipe end at the boundary between the inner and outer pipes. In the heavy pipe structure, when a tensile force is applied to the non-corrosion-resistant pipe side at the pipe ends of the inner and outer pipes, the end face on the corrosion-resistant pipe side and the inner surface on the non-corrosion-resistant pipe side are integrally formed in a ring shape with corrosion-resistant metal. Pre-treatment welding is performed to integrally join the non-corrosion-resistant pipe, and compressive residual stress is applied to the corrosion-resistant pipe, and the inner surface of the pipe end is mechanically machined for a joint, so that the inner surface of the corrosion-resistant pipe is flush with the machined surface for the joint. The end pretreatment welding unit is characterized by a double pipe structure.